The answer is that SW2 became the root bridge because it has the lower MAC address. In the Spanning Tree Protocol root bridge election, the bridge ID is the deciding factor, composed of a configurable bridge priority and the switch’s MAC address. When priorities match—as they do here for VLAN 10—the tie is broken by comparing the MAC addresses, and the switch with the numerically lower MAC address wins, making its overall bridge ID smaller. On the CCNA 200-301 v2 exam, this is a classic STP interpretation question that tests your understanding that the root bridge election is not solely about priority; many learners fall into the trap of assuming equal priorities mean a tie is impossible. A reliable memory tip is to think of the bridge ID as a two-part number: priority first, then MAC address as the tiebreaker—lowest wins both parts.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: sTP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
SW1# show spanning-tree vlan 10
VLAN0010
Root ID Priority 32778
Address 0011.2233.4456
Bridge ID Priority 32778
Address 0011.2233.4456
SW2# show spanning-tree vlan 10
VLAN0010
Root ID Priority 32778
Address 0011.2233.4455
Bridge ID Priority 32778
Address 0011.2233.4455
In a network running STP, SW2 became the root bridge for VLAN 10. Both SW1 and SW2 have the same bridge priority. Why did SW2 become the root?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Because SW2 has the lower bridge ID due to the lower MAC address.
SW2 became the root bridge because its bridge ID is lower. In practical terms, spanning tree elects the root bridge by comparing bridge IDs, which are based on priority plus MAC address. The device with the lowest bridge ID wins. In the exhibit, both switches use the same priority, so the tie is broken by the lower MAC address.
This is a classic STP interpretation question. Many learners focus only on priority, but if priorities match, the MAC address becomes decisive.
Key principle: STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Because SW2 has the lower bridge ID due to the lower MAC address.
Why this is correct
This is correct because the priorities are equal, so the lower MAC address wins the root election.
Related concept
STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.
✗
Because SW2 has the higher VLAN number configured.
Why it's wrong here
This is wrong because VLAN number does not decide the root bridge election.
When this WOULD be correct
In a different question setup where the context involves selecting a root bridge based solely on VLAN configuration, such as asking which switch would be preferred if all other factors were equal and only VLAN numbers were considered, this option could be correct.
✗
Because SW2 has more trunk ports than SW1.
Why it's wrong here
This is wrong because port count does not determine root bridge election.
When this WOULD be correct
In a different question setup, if the question asked why a switch with the most trunk ports would be preferred for forwarding traffic in a network, then this option could be correct. For example, if the question focused on optimizing traffic flow and redundancy in a network design scenario, the switch with more trunk ports might be favored.
✗
Because SW2 has the highest bridge priority.
Why it's wrong here
This is wrong because lower, not higher, bridge ID wins.
When this WOULD be correct
In a different question context where the bridge priority is the only factor being considered, and SW2's bridge priority is indeed higher than that of other switches, this option would be correct. For example, if the question asked which switch would become the root bridge if all other factors were equal but bridge priority was higher for SW2.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Because SW2 has the lower bridge ID due to the lower MAC address.Correct answer▾
Why this is correct
This is correct because the priorities are equal, so the lower MAC address wins the root election.
✗Because SW2 has the higher VLAN number configured.Wrong answer — click to see why▾
Why this is wrong here
The VLAN number is not a factor in the STP root bridge election. The election is based solely on bridge ID, which consists of bridge priority and MAC address.
★ When this WOULD be the correct answer
In a different question setup where the context involves selecting a root bridge based solely on VLAN configuration, such as asking which switch would be preferred if all other factors were equal and only VLAN numbers were considered, this option could be correct.
Why candidates choose this
Students might confuse VLAN numbering with bridge priority or think that higher VLAN numbers have some influence, but STP operates per VLAN with independent elections.
✗Because SW2 has more trunk ports than SW1.Wrong answer — click to see why▾
Why this is wrong here
The number of trunk ports does not affect the root bridge election. STP uses bridge ID (priority and MAC address) to determine the root bridge, not port count or type.
★ When this WOULD be the correct answer
In a different question setup, if the question asked why a switch with the most trunk ports would be preferred for forwarding traffic in a network, then this option could be correct. For example, if the question focused on optimizing traffic flow and redundancy in a network design scenario, the switch with more trunk ports might be favored.
Why candidates choose this
Some might think that more trunk ports indicate a more central switch, but STP does not consider port count in the election process.
✗Because SW2 has the highest bridge priority.Wrong answer — click to see why▾
Why this is wrong here
The root bridge is elected based on the lowest bridge ID, not the highest. A higher bridge priority (numerically larger) makes a switch less likely to become root.
★ When this WOULD be the correct answer
In a different question context where the bridge priority is the only factor being considered, and SW2's bridge priority is indeed higher than that of other switches, this option would be correct. For example, if the question asked which switch would become the root bridge if all other factors were equal but bridge priority was higher for SW2.
Why candidates choose this
Students may mistakenly think 'highest' means best, but in STP, lower values are preferred for both priority and MAC address.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Remember, in STP, lower values are preferred. If priorities match, the MAC address decides the root bridge.
Detailed technical explanation
How to think about this question
Spanning Tree Protocol (STP) is a Layer 2 network protocol that prevents switching loops by electing a single root bridge for each VLAN. The root bridge acts as the logical center of the spanning tree topology. Each switch in the network has a unique Bridge ID (BID), which is composed of a configurable priority value and the switch’s MAC address. STP uses these BIDs to elect the root bridge, with the lowest BID winning the election.
The root bridge election process compares the BIDs of all switches participating in the VLAN. The priority value is the primary factor; if multiple switches share the same priority, the MAC address serves as the tiebreaker. Since MAC addresses are unique and fixed, the switch with the lowest MAC address wins if priorities are equal. This ensures a deterministic and stable root bridge selection. In the exhibit, SW2 became the root bridge because it had the same priority as SW1 but a lower MAC address.
A common exam trap is to assume that the root bridge is always the switch with the lowest priority or the highest VLAN number, or that port count or other factors influence the election. However, STP strictly follows the BID comparison rule, prioritizing lower priority first and then lower MAC address. Practically, this means network engineers can influence root bridge selection by adjusting priority values, but if priorities are equal, the MAC address determines the root. Understanding this helps avoid misconfigurations and ensures predictable STP behavior in Cisco networks.
KKey Concepts to Remember
STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.
The switch with the lowest bridge ID becomes the root bridge for a given VLAN in the spanning tree topology.
If multiple switches have the same priority, STP uses the lowest MAC address as the tiebreaker to elect the root bridge.
VLAN numbers do not influence the root bridge election process in STP.
The number of trunk ports on a switch does not affect the root bridge election decision.
A higher bridge priority value does not help a switch become the root; lower priority values are preferred.
Understanding the bridge ID composition is essential for predicting and controlling STP root bridge election outcomes.
STP root bridge election is deterministic and prevents loops by ensuring a single root per VLAN.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review sTP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address..
What is the correct answer to this question?
The correct answer is: Because SW2 has the lower bridge ID due to the lower MAC address. — SW2 became the root bridge because its bridge ID is lower. In practical terms, spanning tree elects the root bridge by comparing bridge IDs, which are based on priority plus MAC address. The device with the lowest bridge ID wins. In the exhibit, both switches use the same priority, so the tie is broken by the lower MAC address.
This is a classic STP interpretation question. Many learners focus only on priority, but if priorities match, the MAC address becomes decisive.
What should I do if I get this 200-301 question wrong?
Review sTP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
STP elects the root bridge by comparing bridge IDs, which consist of a configurable priority and the switch’s MAC address.
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